The present invention relates to a clamping unit for an injection molding machine.
In injection molding machines, clamping units serve to receive molding tools, mostly constructed in two parts in which in the closed state a plastic melt, which is produced in a plasticizing unit, is injected for the production of a product. Here, the two molding tools must be held together with a great pressure during the injection process. After the cooling and hardening of the plastic product, the clamping unit and therewith the molding tool is opened, in order to be able to remove the product which has thus been produced (DE 10 2004 029 269 A1, WO 2005/118718 A1).
The clamping units are generally classified into so-called two-plate clamping units with one displaceable and one fixed clamping plate, on which the molding tools are clamped, and three-plate clamping units with one fixed and one displaceable clamping plate and one support plate.
In the latter type, generally a drive device acts between the support plate and the displaceable clamping plate, which device is often constructed for opening and closing the clamping unit, but in any case for applying the clamping pressure. The two operating phases of opening and closing on the one hand and of applying the clamping pressure on the other hand differ considerably here in their requirement profile. On opening and closing, the displaceable clamping plate should be moved as quickly as possible, wherein only the mass moments of inertia and frictions must be overcome. This travel movement often also takes place over a longer distance. On applying the clamping force, generally a distance scarcely has to be overcome. The concern here is with applying enormous clamping forces, in order to be able to press the molding tools onto each other with the required force.
In fact in clamping units for large parts, for which a considerable clamping force is necessary, it was usual hitherto to use purely hydraulic drives.
In clamping units for smaller clamping forces (smaller machines), in fact in recent times, however, instead of hydraulic drives electric drives have become established, which have some advantages. Firstly, significant energy savings are possible. These savings are in fact of particular importance in the present time of high energy costs for operating the machine. However, the acquisition costs for electromotive drives increase disproportionately with their size. This has led to the electric motors not being able to become established hitherto in particular in larger machines, because excessively high costs would have to be accepted.